The research outlined in this proposal will enhance our understanding of the neurotransmitters and circuitry of cerebellar afferents, elucidate the effects of ischemia on cerebellar excitatory amino acids (EAAs) and evaluate the efficacy of a novel class of drugs in attenuating ischemic damage. A growing body of evidence suggests that neuronal cell damage following ischemia may result from the excessive release of EAAs. Cerebellar Purkinje cells receive synaptic input from glutamatergic and possibly aspar- tatergic neurons and have been found to be particularly vulnerable to ischemic insult. Thus the cerebellum provides an excellent model to examine the effect of ischemia on putative amino acid transmitter synthesis, release and metabolism and to determine whether major tranquilizers can reduce ischemic damage by their ability to inhibit amino acid synthesis. This proposal will address these issues as well as outline a series of experiments which are an extension of our work during the previous grant period which will examine the anatomical relationships and neurotransmitters of mossy and climbing fiber collaterals to cerebellar output neurons located in the deep cerebellar nuclei. The proposed research will be accomplished by completing the following four specific aims: 1) To analyze the anatomical relationships of and elucidate the neurotransmitters associated with cerebellar afferent fibers that synapse on deep cerebellar nuclear neurons projecting to the thalamus, red nucleus or inferior olivary nucleus; 2) To determine whether the neurotransmitter associated with cerebellar climbing fibers is aspartate and/or glutamate; 3) To determine the effect of ischemia on amino acid concentrations in cerebellar extracellular fluid and on GDH and glutathione immunostaining and to ascertain if changes occur in the mRNA levels of the amino acid synthesizing enzymes GDH, GAD and glutaminase following an ischemic insult; and 4) To evaluate the effect of the major tranquilizers haloperidol, thiothixene and chlorpromazine on amino acid concentrations in extracellular fluid and to determine their ability to attenuate ischemic effects. These studies will generate new data regarding the circuitry and transmitters of cerebellar input fibers and the effects of hypoxia on cerebellar excitatory amino acids. The final portion of this work could indicate a possible therapeutic use of major tranquilizers in the treatment of ischemic neuropathologies, such as stroke and cardiac arrest.